patch 8.0.0478: tests use assert_true(0) and assert_false(1) to report errors

Problem:    Tests use assert_true(0) and assert_false(1) to report errors.
Solution:   Use assert_report().
diff --git a/src/testdir/test_assert.vim b/src/testdir/test_assert.vim
index 0edcf58..8359eb1 100644
--- a/src/testdir/test_assert.vim
+++ b/src/testdir/test_assert.vim
@@ -36,6 +36,12 @@
   call remove(v:errors, 0)
 endfunc
 
+func Test_assert_report()
+  call assert_report('something is wrong')
+  call assert_match('something is wrong', v:errors[0])
+  call remove(v:errors, 0)
+endfunc
+
 func Test_assert_exception()
   try
     nocommand